Various melamine derivatives, as methylene donors, in combination with a methylene acceptor, have been reported for use in forming resin networks, usually in situ, within various rubber compositions to aid, for example, adhesion of the rubber to wire reinforcement. Various of such recited melamine derivatives have been, for example, hexamethoxymethylmelamine (HMMM) and hexaethoxymethylmelamine and N-(substituted oxymethyl) melamine derivatives such as hexakis (methoxymethyl) melamine, N,N′,N″-trimethyl-N,N′,N″-trimethylolmelamine, hexamethyolmelamine, N,N′,N″-trimethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine, N,N′,N″-triethyl-N,N′,N″-tris(methoxymethyl) melamine and N,N′,N″-tributyl-N,N′,N″-trimethylolmelamine.
It is important to appreciate that such melamine derivatives used as methylene donors are often not used in a high purity form and are often a mixture of melamine derivatives. For example, hexamethoxymethylmelamine (HMMM) may actually be a mixture of tetra-, penta-, hexa-OCH2—, and hexa-methoxymethylmelamines and dimers thereof of which the HMMM may typically be the largest individual melamine derivative, or perhaps a major individual melamine derivative in such mixture. For example, the mixture itself may be comprised of from about 25 to about 70 percent HMMM with the remainder comprised primarily of the aforesaid variant melamine derivatives. Thus, while a specific melamine derivative (e.g. the HMMM) may be referred to herein, it is most likely comprised of a blend of melamine derivatives so that a composite or a rubber composition referenced as containing a specific melamine derivative may often more properly be referred to as being comprised of such specified melamine derivative.
Various of reported methylene acceptors have been, for example, resorcinol, phenols, or substituted phenols such as p-isopropylphenol, p-cresol and 4-(p-methyl)phenol, N-(3-hydroxyphenyl) meleamic acid and N-(4-hydroxyphenyl) meleamic acid, phenolic cashew nut oil resin, resorcinol monobenzoate and polyhydric phenoxy resin.
Pre-formed composites of carbon black and various rubber compounding ingredients have heretofore been referred to, for example, to in U.S. Pat. No. 6,053,226 which relates to providing a pre-formed composite of carbon black and rubber compounding ingredient(s), particularly liquid rubber compounding ingredient(s) for use in various rubber compositions. Such rubber compounding ingredients are recited, for example, as liquid coupling agents (liquid bis(trialkoxysilylalkyl) polysulfides), microcrystalline waxes, antiozonants, antioxidants, vulcanization accelerators, and vulcanization inhibitors, and liquid rubber compounding ingredients in The Vanderbilt Rubber Handbook, Thirteenth Edition, 1990, Pages 295 through 395.
In practice, however, liquid melamine derivatives are considered herein difficult to utilize in a commercial rubber manufacturing operation, particularly for use as a combination of a melamine derivative based methylene donor and a methylene acceptor to form a reinforcing resin network within a rubber composition because of inherent processing difficulties relating to mixing the liquid with rubber together with other rubber compounding ingredients in a rubber mixer such as an internal rubber mixer.
Accordingly, it is proposed in this invention to provide such liquid melamine derivative based compound as a particulate, preferably free flowing, pre-formed composite of carbon black and said melamine derivative for use in blending with a rubber composition, particularly as a methylene donor in combination with an addition of a methylene acceptor to the rubber composition to form a reaction product thereof as a resin network in situ within the rubber composition. It is considered herein the carbon black component of the composite may, in part, be incorporated within the in situ formed resin network within the rubber composition.
In the description of this invention the term “phr” refers to parts by weight of an ingredient phr per 100 parts by weight of rubber. The term “rubber” and “elastomer” where used, are interchangeable unless otherwise indicated. The terms “vulcanized” and “cured”, if used, are interchangeable unless otherwise indicated.